I'm going to echo lose the air matress, and put foam under you.

Blast, what is your bag rated to? If it doesn't have one listed, figure about 60 degrees, on the living room couch. :P A better bag, more around your body and head in terms of insulation, and a "snuggle bottle" full of warm-to-hot water. If you fill a lexan bottle with boiling water and cap it, in half an hour is just enough time to make it managable, and it is still pretty toasty two or three hours later. Stuff it in a spare watch cap and it stays snuggly longer.

And there is no shame in admiting you have a snuggle bottle, it takes a man to say that. <img src="/images/graemlins/grin.gif" alt="" />